1. Technical Field
The present invention relates to a method for detecting cracks in a bicycle frame. More particularly, the preset invention relates to a method for detecting cracks in a carbon fiber bicycle frame using an embedded single-mode optical fiber, wherein the single-mode optical fiber is that widely used in fiber-optic communications, which is made of high-purity silicon and has a predetermined diameter (including an acrylic protective layer). By virtue of its small thickness, lightweight, flexibility and capability of transmitting light signals, the single-mode optical fiber can be used as sensors for sensing strain, temperatures, magnetic fields, acceleration, etc.
2. Description of Related Art
Carbon fibers are well known in the art. When consolidated with a predetermined object, the originally lightweight carbon fibers gain extremely high strength and rigidity. Therefore, carbon fibers have been used in various sports equipments including tennis rackets, golf club shafts and bicycle frames. Before consolidation with other objects, carbon fibers are as soft as cloth. When carbon fibers are used to make a bicycle frame, a carbon fiber fabric is placed in a mold, which is then pressurized internally to push the carbon fiber fabric against the mold. Afterward, epoxy is injected into the mold to consolidate the carbon fiber fabric into a desired shape.
Since carbon fibers can provide extremely high strength and rigidity, only a small quantity is needed to make a lightweight and sturdy bicycle frame, wherein a thickness of a carbon fiber layer in the finished bicycle frame can be smaller than about 1 mm. Hence, if cracks exist in the carbon fibers, strain tends to concentrate and may lead to fracture of the frame. A conventional technique for detecting cracks in carbon fibers involves adding loads onto a consolidated carbon fiber bicycle frame so as to detect any distortion of the bicycle frame, thereby determining the existence of internal cracks in an indirect way.
In addition, cracks in a carbon fiber bicycle frame are often associated with excessive torsion of a carbon fiber fabric when placed in a mold to make the bicycle frame. Therefore, another conventional technique for detecting cracks in carbon fibers is to weave a very fine metal wire into a carbon fiber fabric, and trace the metal wire with an electromagnetic sensing method after the carbon fiber bicycle frame is consolidated, so as to determine whether or not the metal wire is partially twisted by the carbon fiber fabric, and thereby predict the possibility that cracks will someday be formed in the carbon fiber bicycle frame. FIG. 1 shows a conventional carbon fiber bicycle frame 10 and distribution of an optical fiber pierced thereinto. As shown in the drawing, a single-mode optical fiber 20 is routed throughout the entire bicycle frame 10 and an optical fiber connector 30 is left inside a socket 101 designed for receiving a bicycle seat so that when it is desired to detect cracks in carbon fibers of the bicycle frame 10, the bicycle seat is removed from the socket to enable access to the optical fiber connector 30. Afterward, the optical fiber connector 30 can be connected with an optical time-domain reflectometer, whose readings are recorded as a basis for determining the possibility that cracks will eventually be formed in the carbon fiber bicycle frame 10.
However, the conventional techniques described above for detecting cracks in carbon fibers are laborious and time-consuming and cannot directly determine the existence of cracks in a bicycle frame.